In recent years, demands for a glass substrate as the base material (substrate) of information recording mediums as represented by a magnetic hard disk drive are increasing.
In order to achieve a higher recording density of an information recording medium, the glass substrate as the substrate is subject to a plurality of polishing steps with a high degree of accuracy such as a rough polishing step, a precision polishing step, and so on. In the foregoing polishing steps, the glass material is demanded of high smoothness and high cleanliness, and the improvement of productivity is also demanded.
As a method of achieving high smoothness, known is the method of using silica-based abrasive grains in the final polishing step, and the cyclic use of the silica-based abrasive grains is known as the means for simultaneously improving the productivity (Patent Document 1). Note that, in the final polishing step, known is the use of a slurry (polishing solution with silica-based abrasive grains dispersed therein) added with a gelling inhibitor for the polishing process in order to prevent clumping of the slurry and gelling (Patent Document 2).    Patent Document 1: Japanese Patent Application Publication No. 2008-246645    Patent Document 2: Japanese Patent Application Publication No. 2008-101132